Transcript of "Plate tectonics"

3.
 Wegener’s continental drift hypothesis stated that the
continents had once been joined to form a single
supercontinent.
 Wegener proposed that the supercontinent, Pangaea,
began to break apart 200 million years ago and form the
present landmasses.

4.
 According to the plate tectonics theory, the uppermost
mantle, along with the overlying crust, behaves as a strong,
rigid layer. This layer is known as the lithosphere.
 There are two types of lithosphere
 Oceanic lithosphere
 Continental lithosphere

7.
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8.
o Plates are moving away from each other
o Midocean ridges are created and new ocean
floor plates are created.
o The plate gives birth to new earth surface
hence it is also called as constructive plate
boundary.
o As new material comes on surface mostly in
sea and increases the sea floor hence it is
called as sea floor spreading.

9.
• Oceanic ridges are continuous elevated zones on the floor of
all major ocean basins. The rifts at the crest of ridges represent
divergent plate boundaries.
• Rift valleys are deep faulted structures found along the axes of
divergent plate boundaries. They can develop on the seafloor or
on land.

11.
The place where two plates move
apart or diverge is called a divergent
boundary.

12.
This is a model of sea floor spreading at a divergent boundary called
a mid ocean ridge.

13.
Did you know that the Earth’s longest mountain range is underwater and
is called the mid-ocean ridge?
: www.ocean.udel.edu
The Mid-Ocean Ridge system, shown above snaking its way
between the continents, is more than 56,000 kilometers (35,000 mi)
long. It circles the earth like the stitching on a baseball!

14.
 A subduction zone occurs when one oceanic plate is
forced down into the mantle beneath a second plate
 Oceanic-Continental
• Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental volcanic arcs form in part by volcanic activity
caused by the subduction of oceanic lithosphere beneath a
continent.
• Examples include the Andes, Cascades, and the Sierra
Nevadas.

15.
• Two oceanic slabs converge and one descends
beneath the other.
 Oceanic-Oceanic
• This kind of boundary often forms volcanoes on the
ocean floor.
• Volcanic island arcs form as volcanoes emerge
from the sea.
• Examples include the Aleutian, Mariana, and
Tonga islands.

16.
• When subducting plates contain continental
material, two continents collide.
 Continental-Continental
• This kind of boundary can produce new mountain
ranges, such as the Himalayas.

19.
 At a transform fault boundary, plates grind past
each other without destroying the lithosphere.
 Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they roughly parallel the
direction of plate movement.
• They aid the movement of oceanic crustal material.

20.
A transform boundary is a place where two plates slip
past each other, moving in opposite directions.

21.
 The plates may move in opposite directions
or in the same directions but at different rates
and frequent earthquakes are created
(example: San Andreas Fault)